The invention relates to a magnetic valve controlled fuel injector for direct fuel injection into a combustion chamber of an internal combustion engine wherein the injector includes a nozzle with a spring-loaded nozzle needle and a control piston with a valve structure at one end for blocking the fuel supply to the nozzle and the control piston is exposed at its other end to the pressure of the fuel in a control space and a magnetic valve by which the control space can be placed into communication with a drain line and open the fuel supply line which leads to the nozzle.
A fuel injection system including such an injector is disclosed in DE 196 12 738 A1, wherein a magnetic valve-controlled control piston of the direct injection fuel injector is in communication with the back side of the spring-loaded nozzle needle. The control piston delimits a control space, which can be connected to the fuel drain line so that, by energizing the magnetic valve, the pressure is released from the control space. When the pressure is released from the control space, the control piston opens a valve whereby the fuel supply line is placed into communication with the nozzle needle.
When such fuel injectors become defective, either by a jamming of the control piston or by a disabled magnetic valve, the high pressure fuel supply line may remain in communication with the injection nozzle which may result in engine damage.
Furthermore, U.S. Pat. No. 5,109,822 discloses a common rail fuel injection system with a direct injection fuel injection valve including a piston which is arranged co-axially with the nozzle needle and which is exposed to the high fuel pressure in the system and acts on the nozzle needle. The piston force causes a rapid closing of the nozzle needle during normal operation.
It is the object of the present invention to provide a high pressure fuel injector with which, by simple measures, engine damage is prevented if the injector becomes defective. In addition, emergency engine operation should still be possible inspite of an injector being defective.